With rapid development of remote and wireless sensor network, continuous power supply is becoming the limiting factor for the lifetime of the device as depletion of the attached battery power. For example, in precision agriculture, sensors are normally located in a distant plantation and powered up by a battery which has limited capacity and lifetime to supply power for the sensors. Therefore, for a self-contained sensor or processing circuit to attain truly autonomous, renewable on-board power supply is required. One way to eliminating use of exhaustible battery from the device is through continuous energy harvesting from a sustainable source. Energy harvesting is the process by which energy is captured and stored also known as power harvesting or energy scavenging. Such approach is especially useful for small autonomous devices, like those used in sensor networks so that they are portable and require little power. However, energy harvesting involving a single source is usually insufficient to completely and continuously to power the electronic system. Therefore, it is desired to have a hybrid energy harvesting system to acquire energy from different sustainable source.
Worldwide patent application no. 2007070022 claims an ambient energy harvesting system comprising a magnetic flux-generating assembly, a coil positioned adjacent to the magnetic flux-generating assembly, and a cantilevered arm which vibration enables relative movement between magnetic flux-generating assembly and the coil to generate an electric current in the coil.
Mitchell et al. provides an energy harvesting device in United States Patent publication no 2008092937. The claimed device comprises a fastening device, a first thermally-conductive element engaging the fastening device, a thermoelectric device disposed in thermal contact with the first thermally-conductive element, a thermoelectric device disposed in thermal contact with the first thermally conductive element, and a second thermally-conductive element disposed in thermal contact with the thermoelectric device.
Further in United States patent application no 2008100180, an apparatus capable of harvesting energy through small vibration amplitudes over a wide frequency band. The disclosed apparatus comprises a beam including an electrically responsive material with attachment structure for enabling the beam to be coupled to an external structure experiencing vibration; a force biasing member disposed adjacent the beam; a support structure for engaging each of the beam and the biasing member to apply compressive force wherein the beam adapted to flex in response to vibration from the external structure to generate electrical signal.